Corrosion-inhibited and stabilized perfluorinated polyether oils



United States Patent 3,518,195 CORROSION-INHIBITED AND STABILIZEDPERFLUORINATED POLYETHER OILS Bruce H. Garth, Newark, Del., assignor toE. I. du Pont de Nemours and Company, Wilmington, Del., a corporation ofDelaware No Drawing. Filed June 5, 1968, Ser. No. 734,571 Int. Cl. (310m1/32 US. Cl, 25251.5 6 Claims ABSTRACT OF THE DISCLOSURE Corrosionanddegradation-inhibited oil compositions comprising a perfluorinatedpolyether oil and a substltuted guanamine of the structure where R; isperfluoroalkyl and m is an integer.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to stabilized perfluorinated polyether oils. More particularly,the invention is directed to such oils containing sufficient amounts ofperfluoro- 0x0 or perfluoropolyoxoalkane substituted guanamine additivesto inhibit corrosion and oil degradation.

Description of the prior art A need for lubricating oils which willremain serviceable for long periods of time at temperatures above 500 F.(260 C.) has long existed. The perfluoropolypropoxy polymers, i.e.,polymers having the recurring group and which are end-capped withperfluoroalkyl groups have been found to approach the desiredperformance characteristics stated above. By fractionation, oilyfractions of such polymers are obtained which are operable aslubricating Oils at temperatures as high as 800 F. (427 0.). Such Oilshave no apparent efifect on metals and do not evidence degradation attemperatures up to about 400 F. (204 (1.); however, at temperaturesabove 500 F. (260 C.), both metal corrosion and degradation of the oiloccur. Representative metals which have been shown to corrode with suchoils include steel, stainless steel, aluminum, titanium and titaniumalloys. Accordingly, it is desirable, and it is one object of thisinvention, to provide these oils with an additive which eliminates orreduces both metal corrosion and oil degradation at extremely hightemperatures; e.g., from 500 F. to 700 F. (371 C.).

To perform as an acceptable additive, the additive must haveadditionally acceptable properties over and above the properties ofretarding corrosion and degradation. The additive must be compatiblewith the oil and have little, if any, effect on the lubricatingproperties of the oil, such as its lubricity, viscosity and viscosityindex. It is another object of this invention to provide such acompatible additive. In addition, the additive must be soluble in theoil to an extent which produces an effective concentration for itspurpose. The solubility Patented June 30, 1970 must be such that theadditive will not separate from the oil, either at high operatingtemperatures or at low (ambient) storage or non-operating temperatures.The additive must also possess a high degree of thermal stabilityitself. It is still another object of this invention to provide anadditive which possesses such desirable solubility and thermalproperties with the perfluoropolypropoxy oils.

SUMMARY OF THE INVENTION The novel compositions of this invention areperfluorinated polyether oil compositions comprising:

(a) A perfluorinated polyether oil selected from the class consisting ofoils of the structure In (Em and CF3 3 CF3 wherein R; is defined asabove and m is an integer of 0 through 100.

DETAILED DESCRIPTION OF THE INVENTION (A) The perfluorinated polyetheroils The base oils employed in the compositions of this invention areperfluorinated polyethers which may be derived from hexafluoropropyleneoxide. These oils are prepared by first polymerizing hexafluoropropyleneoxide, either alone or in the presence of a carbonyl fluoride, aperfluoro acid fluoride or a perfluoro ketone, using certain fluorideion containing catalysts or charcoal as taught by Moore et al7 in US.Pat. 3,250,808, by Moore in Canadian Pat. 707,359, by Fritz et al. inUS. Pat. 3,250,807, by Moore in Canadian Pat. 707,361, and US. Pat.3,322,826 and by Selman in US. Pat. 3,274,239 to obtainhexafluoropropylene oxide polymers of the structure:

where R is a perfluoroalkyl group and n ranges from 0 to 100. Thesepolymers are readily hydrolyzed in the presence of water to thecorresponding acids of the structure:

R O [CF (CF CF 0 CF CF COOH These acids are converted to perfluorinatedpolyethers by reaction with elemental fluorine according to theprocedure of Miller in US. Pat. 3,242,218 to give products of thestructure:

These polymers may also be converted to perfiuorinated polyethers byultraviolet light coupling with the elimination of the COP group astaught by Milian U.S. Pat. 3,214,478 to form oils of the structure:

The hcxafluoropropylene oxide polymers may also be converted to productscontaining a single hydrogen of the structure:

as taught by Selman et al. in U.S. Pat. 3,342,875, but the presence ofthe hydrogen causes the resulting oils to be less desirable than thosederived from the perfluorinated ethers.

Alternatively, as taught by Sianesi et al. in French Pat. 1,434,537,perfiuorinated polyethers exemplified by the structures,

may be prepared from perfiuoropropylene. Such materials may be convertedto useful perfluorinated polyether oils by one or more of the methodsfor end-capping in the patent references mentioned above in thissection. Thus it is seen that n in the oils employed herein ispreferably between 1 and 100.

As indicated above, the perfiuorinated polyether polymers may vary fromlow molecular weight products to very high molecular weight products. Tobe useful in the present invention, the perfiuorinated polyesters mustbe chosen from this broader class of compounds to meet the requirementsof volatility and pour point which are necessary to obtain useful oils.The oils must have a maximum volatility of 50% at 204.4 C. (400 F.) asdetermined by Federal Test Method FTMS-79l, Method 351 and a maximumpour point of C. (50 F.) as determined by ASTMD-97. Within this class ithas been found that oils having molecular weights of 3000 to 13,000 arepreferable. Of course, the polymerization methods give mixtures ofproducts so that the molecular weights are an average. Although a pureproduct having a specific molecular weight may be used, mixtures ofproducts are equally useful if the variation in molecular weight is nottoo large. Usually, the most volatile lower molecular weight materialsare removed from oils before use.

Oils having volatilities greater than that specified above are notuseful because they do not have the service life required. Oils havingpour points greater than 10 C.

are not useful because, under many startup conditions,

they would be too thick to provide lubrication before equipment in whichthe oils are being used had heated sufficiently to permit adequate oilflow to contacting metal surfaces.

Particularly preferred oils have the structure,

R O [CF (CF CF 0] CF CF where R is a perfluoroalkyl group of from 1 toabout 4 carbons, and which have a molecular weight range of from about4500 to about 7000, and pour points of from about -10 to about 40 C.

(B) The substituted guanamine additives where m is 0 to 100, R, is Cperfluoroalkyl and R is a lower alkyl, e.g., a methyl or ethyl group,with biguanide 4 under alkaline catalysis. This preparation is morefully described in applicants assignees copending application, Ser. No.734,546, filed concurrently herewith.

These substituted guanamines are used in an effective amount in theperfluorinated polyether oils. By effective amount is meant the amountrequired to produce useful inhibition of metal corrosion and oildegradation for the required service life of the device containing theoil at the desired operating temperature. Various metals differconsiderably in the amount of corrosion which will occur and inpromoting effect on oil degradation. Thus, the effective amount ofadditive will vary with the service and with the metals in contact withthe oils.

In general the amount of the substituted guanamines required will be inthe range of from about 0.1% by weight of the oil to about 8% by weight.At less than 0.1% concentration there is seldom enough additive toperform effectively. Additive concentrations above 8% seldom produce anyincrease in eflectiveness. For a general purpose high-temperature oil itis usually preferable to add between about 2% and about 6% by weight ofthe substituted guanamines. This range provides for the vast majority ofthe needs for the oils.

Most preferably, the substituted guanamines are those in which m is aninteger of 3 through 30.

The compositions of this invention are prepared by simply mixing thesubstituted guanamine with the perfiuoroinated polyether oil in theselected amounts.

(C) Examples The following examples, illustrating the novel compositionsof the invention and their effectiveness, are given without anyintention that the invention be limited thereto. All percentages are byweight.

Compositions of this invention were tested using a modified form of theapparatus specified in the WADD Microoxidation-Corrosion Test of HighTemperature Fluids, Fluids and Greases Section, Aeronautical Systems,Wright-Patterson Air Force Base, replacing the specified Pyrex tube withan Inconel tube. Basically the apparatus consists of a 3.18 mm. diameterInconel tube adapted for mounting three washers outside the lower end.The 3.18 mm. tube is inserted inside a 20.6 diameter vertical Inconeltube so that the washers are immersed in a body of oil contained in thelarger tube. The larger tube, which is adapted with a condenser forrecovering any oil which may be stripped from the tube, is inserted inan aluminum heating block.

Various metal washers of the compositions in the following Table I weretested:

TABLE I Metal in washers Composition Group A. Titanium alloys- Ti(6A1-4V) 6% A1, 4% V; balance Ti.

Ti (A-70) Essentially Ti.

Group B. Ferrous alloys (steels 410 0.15% C, 12% Cr, 1% Mn, 1% Si.

440C 1.1% C, 17% Cr, 1% Mn, 1% Si, 0.75%

Mo; balance Fe.

M-2 47%Cr, 2% V, 0.3% W, 5% Mo; balance 52100 1% C, 1.4% Cr, 0.3% Mn,0.2% Si;

balance Fe.

4140 0.4% C, 0.9% Cr, 0.9% Mn, 0.3% Si,

0.2% Mo; balance Fe.

0.8% C, 4% Cr, 0.25% Si, 4.5% M0,

0.1% Ni, 1% V; balance Fe.

The test consisted of placing test washers of the metals to be tested inthe apparatus, adding sufiicient oil composition to insure that thewashers are covered, assembling the remaining apparatus and inserting itin the heating block. The oil is then heated to the test temperature andair is passed down through the smaller tube into the body of oilcontaining the washers. Test duration was 72 hours. Air flow rate intothe oil during the test was 5 liters per hour, measured at 25 C.

Percent viscosity change cs after test cs before test cs before test X100 where cs. is the kinematic viscosity, at 37.78 C., in

inated substituent side chain of the substituted guanamine additives:

TABLE II.OIL DEGRADATION AT SELECTED TEMPERATURES 72 hour fluid loss andviscosity change 315 .6 0. (600 F.) 343.3" C. (650 F.) Wt. percentpercent percent percent percent Additive Example additlve fluidviscosity fluid viscosity solubility No. In Metal present loss changeloss change at 25 C.

1 O 2 13 A l 1. 5 13 2. 8 13 5. 8 5. 7 13 0 13 B 9 0.8 13 2.8 13 5. 8 205. 7 11 Ti (6A1, 4V) 0 12 4 Ti (6A1, 4V) 4. 3

5 The A group of Table I tested together. 2 The B group of Table Itested together. 3 All Washers in these test were Tl (6A1, 4V).

centistokes. When the sign of the percent viscosity change is negative,oil degradation is indicated. When the sign is positive, hightemperature loss of volatile oil compo- The data in Table II shows theeffectiveness of the substituted guanamines in reducing oil degradationat 315.6" C. and at 343.3 C., respectively.

TABLE IIL-CORROSION INHIBITION Washer wt. change, mgJcmfl/day nents isindicated. It will be noted in the following Table II that oildegradation is frequently accompanied by increased fluid loss from theapparatus. Degradation of polymer chains provides fragments havinggreater volatility than the original polymer.

Corrosion is determined by weighing the test washers before and afterthe test. Corrosion rate is calculated from weight change and knownwasher surface area. Before weighing, both before and after the test,the test washers are cleaned by scrubbing with scouring powder andwater, rinsed with water, degreased and dried with acetone. The oil usedin the following examples has the structure.

where n is sufiiciently large to afford an oil with an average molecularweight of about 5000.

In the following Tables II and III the letter in refers to the averagedegree of polymerization in the perfluor- The data in Examples 13 to 30of Table III demonstrate the effectiveness of the additives in reducingor preventing corrosion of titanium, titanium alloys, and ferrousalloys. Additive effectiveness is particularly marked at the higher ofthe two test temperatures. The other steels of Table I, 52100, 4140 andM-SO show little or no corrosion at 315.6 and at 343.3 C.

Similar results may be obtained with oils of the structure clearness ofunderstanding only and no unncessary limi- (JFK and

o F; C F;

wherein R is perfiuoroalkyl of 1 through 6 carbon atoms, R isperfiuoroalkyl of 1 through 2 carbons and n is an integer denoting thedegree of polymerization; said oil having an average molecular weight ofat least 3000, a pour point of less than 10 C., and a maximum volatilityof less than 50% at 204.4 C.; and (b) a substituted guanamine of thestructure wherein R is defined as above and m is an integer of 0 through100 present in an amount eifective for corrosion inhibition andstabilization.

2. The composition of claim 1 wherein the substituted guanamine ispresent in an amount of between about 0.1 to about 8 percent by weightof the perfiuorinated polyether oil.

3. The composition of claim 2 wherein the perfiuorinated polyether oilhas the structure rt Hi0 \(Jl Clz O/u wherein R is perfluoroalkyl of 1through 6 carbon atoms, R is perfluoroalkyl of 1 through 2 carbon atoms;and n is an integer of between 1 and 100.

4. The composition of claim 3 wherein R CF CF 5. The composition ofclaim 4 wherein R is and the oil has an average molecular weight ofbetween about 4500 and 7000.

6. The composition of claim 5 wherein m in the substituted guanamine isan integer of 3 through 30, and wherein the substituted guanamine ispresent in an amount of between about 2 to about 6 percent by weight ofthe perfiuorinated polyether oil.

References Cited UNITED STATES PATENTS 2,680,717 6/1954 Little 25251 X3,306,854 2/1967 Gumprecht 252t-49.9 3,453,275 7/1969 Grindahl et a1252-51 X DANIEL E. WYMAN, Primary Examiner W. J. SHINE, AssistantExaminer U.S. C1. X.R. 252-392, 403

